To get started with Android/LineageOS, you'll need to get familiar with Repo and Version Control with Git.
To initialize your local repository using the LineageOS trees, use a command like this:
repo init -u https://github.com/LineageOS-Revived/android.git -b lineage-17.1 --git-lfs
Then to sync up:
repo sync
Please see the LineageOS Wiki for building instructions, by device.